Study On The Mechanism And Application Of Potassium Phosphate Improving The Acidification Of Tea Garden Soil

Due to the long-term excessive application of chemical fertilizers and nitrogen fertilizers in tea gardens,the problem of soil acidification in tea gardens has become increasingly prominent.In order to find out the action path of potassium phosphate to improve the acidification of tea garden soil and its application effect in tea garden soil.In this experiment,three kinds of tea garden soil with different acidity（pH3.53,pH4.16,pH4.53）were used,and four concentration levels of potassium phosphate treatment were set,which were 50 mg/kg（K₁）and 100 mg/kg（K₂）,150 mg/kg（K₃）,200mg/kg（K₄）,with no fertilization as the control（CK）,an indoor soil culture test was conducted to determine the contents of soil pH,exchangeable cations,ammonium nitrogen and nitrate nitrogen.,to analyze the effect of potassium phosphate fertilizer application on the above indicators,and to explore its improvement effect and mechanism of action by constructing a structural equation model.Based on this,the experiment of potassium application in tea garden was carried out to further clarify the application effect of potassium phosphate fertilizer on soil pH,exchangeable cationic nutrients and tea quality and yield.The main conclusions are as follows:（1）The addition of potassium phosphate has a significant improvement effect on soil acidification in tea gardens.Potassium phosphate can significantly increase soil pH and exchangeable K+content in acidified tea garden soil in a short period（20 days）,reduce exchangeable A1³⁺content,and affect the relationship between ammonium nitrogen（NH₄⁺-N）and nitrate nitrogen（NO₃^--N）at the same time.The improvement effect became more significant with the increase of potassium phosphate concentration,and the pH increase was the most significant when the addition concentration was 200 mg/kg.For soils with pH of 3.53,4.16,and 4.53,the soil pH after potassium application increased by 0.17,0.19,and 0.23 units,respectively,and the exchangeable K⁺increased by 105%,101%,and 135.46%,respectively.decreased by0.46,0.64,and 0.29 cmol/kg,NH₄⁺-N decreased by 49.66%,46.68%,41.12%,and NO₃^--N increased by 168.07%,74.34%,and 82.6%,respectively,indicating that nitrification of NH₄⁺-N occurred during the cultivation period.Therefore,the acidification improvement of potassium phosphate has short-term effect.（2）The main paths of adding potassium phosphate to improve soil acidification in tea garden were the direct path of exchangeable K⁺to pH and the indirect path of exchangeable Al³⁺to pH and exchangeable Na⁺and Ca²⁺to pH.The direct path has a significant positive effect on pH by increasing the exchangeability K⁺,and the path coefficient is 0.7515.Exchangeable K⁺also produces two indirect paths to pH by influencing other base ions and exchangeable Al³⁺.One is the indirect path by which exchangeable K⁺produces a negative effect and acts as exchangeable Al³⁺to reduce aluminum content and thus indirectly improve pH.The path coefficient is-0.2427.The other is that exchangeable K⁺influences exchangeable Ca²⁺by increasing exchangeable Na⁺to eventually improve pH,and the path coefficient is 0.2721.Moreover,exchangeable K⁺is the dominant factor controlling acidizing improvement,exchangeable Al³⁺is the main acid-causing factor,and exchangeable Na⁺and Exchangeable Ca²⁺are the regulatory factors controlling acidizing improvement.The three factors jointly acted on soil pH and finally improved acidified soil.（3）Application of potassium phosphate can not only improve soil acidification,but also enhance soil fertility and improve tea yield and quality.Compared with conventional fertilization in tea garden,the soil pH of K1（30 kg/mu）and K2（60 kg/mu）treatments increased by 0.47 and 0.28units on average.The exchangeable potassium and available potassium of K1 treatment increased by 270.90%and 646.58%,respectively,and the exchangeable potassium of K2 treatment increased by 502.99%and1166.29%,respectively.The content of soil available P under K2 treatment increased by 69.26%compared with CK.K application also increased the organic matter content of tea garden soil in summer by 14.15%compared with CK.Multiple application of potassium phosphate can effectively reduce exchangeable H⁺content and exchangeable Al³⁺content fluctuation in acidified soil.The application of potassium phosphate in tea garden can increase the yield of summer tea and improve the quality of spring tea.Low concentration（K1）potassium phosphate increased the 100 bud weight of summer tea in acidified tea garden by 15.18%compared with CK,while high concentration（K2）potassium phosphate increased the germination density and yield per unit area of summer tea by 26.87%and 18.36%,respectively.K1 treatment can effectively reduce the tea polyphenol content in summer tea,and K2 treatment can increase the total free amino acid content of spring tea by 7.4%.Tea yield was positively correlated with soil pH,exchangeable K⁺and Al³⁺,and negatively correlated with tea polyphenol content.Exchangeable⁺was negatively correlated with tea yield.Tea water extract was positively correlated with exchangeable Na⁺,Ca²⁺and Al³⁺,and exchangeable Na⁺was negatively correlated with free amino acids and caffeine.To sum up,the addition of potassium phosphate has a good effect on the improvement of soil acidification in tea gardens.The main direct path of the improvement is to increase the exchangeable K⁺to have a significant positive effect on pH.There are two indirect paths.The exchangeable Al³⁺has a negative effect to reduce the aluminum content,which has an indirect negative effect on pH;the second is that the exchangeable K⁺affects the exchangeable Ca²⁺by increasing the exchangeable Na⁺,and finally the exchangeable Ca²⁺has an indirect positive effect on pH.Exchangeable K⁺is the main control factor of acidification improvement pathway,exchangeable Al³⁺is the main acidogenic factor,and exchangeable Na⁺and exchangeable Ca²⁺are the regulatory factors.The application of potassium phosphate in tea gardens can improve soil acidification and also improve soil fertility.After potassium application,the contents of soil pH,exchangeable K⁺,available potassium and available phosphorus are significantly increased,and soil exchangeable Al³⁺and H⁺have decreased,thus improving summer tea.yield and improve the quality of spring tea leaves.Therefore,in practical application and production,it is necessary to apply potassium fertilizer according to local conditions.For tea gardens with serious soil acidification and potassium deficiency,it is suggested that30 kg/mu of potassium phosphate can be applied in a short term.